Preparation of metal nanowire decorated carbon allotropes

ABSTRACT

In the method of embodiments of the invention, the metal seeded carbon allotropes are reacted in solution forming zero valent metallic nanowires at the seeded sites. A polymeric passivating reagent, which selects for anisotropic growth is also used in the reaction to facilitate nanowire formation. The resulting structure resembles a porcupine, where carbon allotropes have metallic wires of nanometer dimensions that emanate from the seed sites on the carbon allotrope. These sites are populated by nanowires having approximately the same diameter as the starting nanoparticle diameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 11/710,386, filed Feb. 23, 2007, issued as U.S.Pat. No. 7,704,553. This patent application claims the benefit of U.S.Provisional Patent Application No. 61/327,189, filed Apr. 23, 2010.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made in part by employees of the United StatesGovernment and may be manufactured and used by or for the Government ofthe United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

The present invention relates generally to metallic nanowire decoratedcarbon allotropes, and specifically to methods of preparing suchallotropes and dispersing them into polymeric matrices.

It is known that materials with improved mechanical properties, such asthermal conductivity, can be created by blending metallic nanowires,with various polymers. In these methods, metallic nanowires weresynthesized by a templateless method, isolated, and subsequently blendedwith various polymers. However, in these methods, the inclusion of thenanowires into an organic matrix was hampered by poor dispersability ofpure nanowire additives into polymeric matrices. Continuous ways arebeing sought to take advantage of metallic nanowires and incorporatesuch materials into composite polymeric matrices.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to providemethods of using carbon allotropes as anchors on which to grow surfacemetallic nanowires and to alleviate processing problems encountered withpure nanowire additives in polymeric matrices. The homogeneousdispersion of carbon allotropes into polymeric matrices has generallybeen mastered and similar techniques can be used to processnanowire-carbon allotrope polymer composites.

It is a related object of the invention to provide the ability to usenanometer-sized particles of metals seeded onto carbon allotropes as asource of starting material to prepare the metal decorated allotropes,which may be used as novel materials or tailored into specific catalystsor even ultimately modified to create a polymeric matrix reinforced withsuch allotropes.

These objects are achieved by the present invention, which provides inone embodiment a method of preparing metal nanowire decorated carbonallotropes comprises providing a plurality of seed templates, each seedtemplate comprising a carbon allotrope containing a plurality ofmetallic crystalline seeds; and reacting the plurality of seed templatesin solution with a polymeric passivating reagent to form a zero valentmetallic nanowire from each metallic crystalline seed. The carbonallotrope may be selected from the group consisting ofbuckminsterfullerene, carbon nanotube, graphite, and exfoliatedgraphite. The metallic crystalline seeds may be selected from the groupconsisting of silver, gold, platinum, palladium, and nickel. The methodmay further comprise controlling a diameter of the metal nanowires bycontrolling a diameter of the metallic crystalline seeds. The method mayfurther comprise controlling a density of the metal nanowires bycontrolling a density of the metallic crystalline seeds.

In another embodiment of the invention, a method of preparing apolymeric matrix comprises preparing a plurality of metal nanowiredecorated carbon allotropes and dispersing the plurality of metalnanowire decorated carbon allotropes in a polymer. Preparing a pluralityof metal nanowire decorated carbon allotropes may comprise providing aplurality of seed templates, each seed template comprising a carbonallotrope containing a plurality of metallic crystalline seeds; andreacting the plurality of seed templates in solution with a polymericpassivating reagent to form a zero valent metallic nanowire from eachmetallic crystalline seed. The carbon allotrope may be selected from thegroup consisting of buckminsterfullerene, carbon nanotube, graphite, andexfoliated graphite. The metallic crystalline seeds may be selected fromthe group consisting of silver, gold, platinum, palladium, and nickel.The method may further comprise controlling a diameter of the metalnanowires by controlling a diameter of the metallic crystalline seeds.The method may further comprise controlling a density of the metalnanowires by controlling a density of the metallic crystalline seeds.

In yet another embodiment of the invention, a polymeric matrix comprisesa plurality of metal nanowire decorated carbon allotropes homogeneouslydispersed inside a polymer. The plurality of metal nanowire decoratedcarbon allotropes may be prepared by a method that comprises providing aplurality of seed templates, each seed template comprising a carbonallotrope containing a plurality of metallic crystalline seeds; andreacting the plurality of seed templates in solution with a polymericpassivating reagent to form a zero valent metallic nanowire from eachmetallic crystalline seed. The carbon allotrope may be selected from thegroup consisting of buckminsterfullerene, carbon nanotube, graphite, andexfoliated graphite. The metallic crystalline seeds may be selected fromthe group consisting of silver, gold, platinum, palladium, and nickel.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a drawing prepared from a high resolution scanning electronmicrograph (HRSEM) of a metal nanowire decorated carbon allotropeprepared employing the exemplary procedure detailed below.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention provide a novel polyol soft solution methodfor producing metallic nanowire decorated carbon allotropes, therebyenabling the production of novel polymeric matrices and the developmentof material systems and with improved thermal conductivity (among otherbenefits such as, but not limited to, physical, mechanical and/orelectrical properties).

Embodiments of the invention enable nanowire growth of a variety ofmetals on a variety of metal seeded carbon allotropes. The metalliccrystalline seeds serve as growth sites for the metal nanowires. Themetals include but are not limited to silver, gold, platinum, palladium,and nickel. The carbon allotropes include but are not limited tobuckminsterfullerene, carbon nanotube, graphite, and exfoliatedgraphite. Methods of embodiments of the invention provide a versatileway of producing metallic nanowires of controlled diameter sizes anddistribution density on the surface of carbon allotropes. The net resultis that the nanowire density and the nanowire-to-carbon allotrope ratiocan be adjusted to adjust the properties needed for specificapplications.

Embodiments of the invention may use metal decorated carbon allotropesproduced using the methods described in U.S. Pat. No. 7,704,553, thecontents of which are incorporated herein in their entirety. However,the method of embodiments of the invention is not limited to using themetal decorated carbon allotropes produced using the methods describedin U.S. Pat. No. 7,704,553. Any metal seeded carbon allotrope,regardless of method of preparation, can be used as a starting material.

In an exemplary aspect, a process preparing metal seeded carbonallotrope templates begins with depositing very small (viz.,nanometer-sized) metal particles onto a substrate (such as a carbonallotrope) in the absence of aqueous solvents, organic solvents, andreducing agents, and without any required pre-treatment of thesubstrate. An admixture of a metal compound and a substrate is preparedby dry mixing a chosen amount of a metal compound with a chosen amountof a substrate. Energy is then supplied to the admixture in an amountsufficient to reduce the metal ion in the metal compound to a valence ofzero. Dry mixing of the metal compound and the substrate is preferablycontinued until substantial uniformity of the admixture is achieved, asdetermined, for example, by visual inspection. A wide variety ofstandard dry mixing techniques may be employed, including, but notlimited to grinding with a mortar and pestle, mechanical shaking, ballmilling, and ultrasonic agitation, among many others. After mixing iscomplete, energy is supplied to the admixture, advantageously in theform of heat, as supplied by a standard oven. However other forms ofenergy may be employed with success such as microwave energy, as in amicrowave oven, among others. The atmosphere surrounding the admixturemay be air, or an inert gas such as nitrogen. If a standard oven inemployed, a preferred temperature for heat treatment is from about 250degrees Celsius to about 350 degrees Celsius, for a time between about0.5 hours to about 6 hours, with about 2 hours to about 4 hours beingpreferable. Although a number of substrates may be employed in theinstant process, carbon allotropes have been used very advantageously.Carbon allotropes are structurally differentiated forms of the elementcarbon. Examples of acceptable carbon allotropes are: amorphous carbon,carbon nanofibers, carbon nanofoam, diamond, fullerene, graphite,exfoliated graphite, single-walled carbon nanotubes, multi-walled carbonnanotubes, double-walled carbon nanotubes, Ionsdaleite and aggregateddiamond nanorods. Preferred carbon allotropes are: amorphous carbon,graphite, exfoliated graphite, single-walled carbon nanotubes,double-walled carbon nanotubes, and multi-walled carbon nanotubes.Preferred metals are those listed in the periodic table as transitionmetals of Group VIIIA (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt), those ofGroup IB (Cu, Ag, and Au) and those of Group IIB (Zn, Cd, and Hg),including mixtures thereof. The metals Pd, Pt, Ag, and Au are especiallypreferred. The metals are in the form of a compound with another elementor group. Preferable elements in the metal compound are halides,especially chloride. Preferable groups in the metal compound are organiccarboxylates, and especially acetates. The concentration of the metalcompound relative to the substrate, e.g., the carbon allotrope,influences the particle size of the metal that is subsequentlydeposited. Metal compound concentrations that ultimately result in finalzero valence metal particle concentrations on the carbon allotrope of upto 50% by weight are preferable. The compositions are characterized byhigh resolution scanning electron microscopy (FIRSEM) to determine metalparticle size and distribution. The oxidation state of the metal isdetermined by x-ray photoelectron spectroscopy and/or wide angle x-raydiffraction.

The exemplary seed template compositions comprised of metal particlesdistributed onto the surfaces and/or within the interstices of varioussubstrates, especially various forms of carbon, of the present inventioncan ultimately be used to produce polymer composites by combining themwith commodity and engineering plastics to produce novel materials withadvantageous characteristics. The term “polymer composites”, as usedherein, refers to a composition that comprises at least one substrate,e.g., one form of carbon with metal particles distributed thereon and atleast one polymer. The polymer matrix or matrices may be commodity orengineering plastics such as polycarbonate, polyacrylate,polyacrylonitrile, polyester, polyamide, polystyrene (including highimpact strength polystyrene), polyurethane, polyurea, polyurethaneurea,polyepoxy, poly(acrylonitrile butadiene styrene), polyimide,polyarylate, poly(arylene ether), polyethylene, polypropylene,polyphenylene sulfide, poly(vinyl ester), polyvinyl chloride,bismaleimide polymer, polyanhydride, liquid crystalline polymer,cellulose polymer, or any combination thereof. These are commerciallyavailable from, for example, GE Plastics, Pittsfield, Mass.; Rohm & HaasCo., Philadelphia, Pa.; Bayer Corp.—Polymers, Akron, Ohio; Reichold;DuPont; Huntsman EEC, West Deptford, N.J.; BASF Corp., Mount Olive,N.J.; Dow Chemical Co., Midland, Mich.; GE Plastics; ExxonMobil ChemicalCorp., Houston, Tex.; ExxonMobil/Mobay Chemical Corp., Kansas City,Kans.; Goodyear Chemical, Akron, Ohio; BASF Corp.; 3M Corp., St. Paul,Minn.; Solutia, Inc., St. Louis, Mo.; DuPont; and Eastman Chemical Co.,Wilmington, Del. and Kingsport, Tenn., respectively). The polymercomposites are produced via standard blending, mixing, or compoundingthe constituent materials. The polymer composites of the presentinvention may comprise other components, such as fillers, surfactants,organic binders, polymeric binders, crosslinking agents, couplingagents, anti-dripping agents, heat stabilizers, antioxidants, colorants,inks, dyes, or any combination thereof. The polymer composites of thepresent invention are used as coatings, or they are used to fabricatearticles, such as free-standing films, fibers, fabrics, foams, moldedand laminated articles, tubes, adhesives, and fiber reinforced articles.These articles are well-suited for many applications requiring thermalconductivity, electrical conductivity, antibacterial activity, catalyticactivity, and combinations thereof.

Synthesis of metallic nanowires or nanorods in accordance withembodiments of the invention use a synthetic method of which zero valentmetal nanometer sized clusters serve as the seed for unidirectionalgrowth of metallic nanowires. The radii of resulting nanowires arecontrolled via the diameter of the metal “seeds” from which the nanowiregrowth commences. The seeds can be introduced via in-situ method fromwhich the nanowires are grown, or they can be introduced via metallicnanometer-decorated substrates, such as those described herein, ofmetallic decorated carbon allotropes. The metallic clusters on thecarbon allotropes become the “seed sites” from which nanowire growthoccurs. This synthetic process is particularly useful where theproperties unique to high aspect ratio additives are desirable in ahybrid material and enhanced further through functionalized metalnanowires. Traditional methods of hybrid material preparations aredifficult to extend to nanometer sized additives, in particular,dispersion issues render a non-homogenous hybrid material withinconsistent physical properties, and ultimately not fit for manyconceivable applications. This invention circumvents those problemswhere nanometer-sized carbon allotropes are desired within a hybridsystem, along with the additional properties that are desired specificto zero-valent nanocluster, nanorods, or nanowires which enhance ahybrid material system, and extend the applications for such materialuse.

In at least some embodiments of the invention, the metal seeded carbonallotropes are reacted in solution, forming zero valent metallicnanowires at the seeded sites. The preferred polyol solvent used (forexample, ethylene glycol) can be both the solvent and reducing agent. Apolymeric passivating reagent, which selects for anisotropic growth, isalso used in the reaction to facilitate nanowire formation. Such anexemplary passivating reagent is poly (vinyl-pyrolidone), whichfunctions as the capping or passivating agent. Other similar solvents,reducing agents, capping and/or passivating agents may be selected basedon similar chemical functionalities as known to those of ordinary skillin the art. The instantly inventive reaction, carried out in thepresence of metal decorated carbon allotropes, initiates the synthesisof coordinated metallic growth from each “seed” from which eachunidirectional nanowire emerges. Metal decorated carbon allotropes serveas the substrate here, and the nanometer-sized metal decorations serveas “seed sites” for synthesis of nanowires which are anchored to theselected carbon substrate. The resulting structure resembles aporcupine, where carbon allotropes have metallic wires of nanometerdimensions that emanate from the seed sites on the carbon allotrope.These sites are populated by nanowires having the same diameter as thestarting nanoparticle diameter. The metal seeded carbon allotropesprovide reliable and homogenous seed diameters. The density of nanowirescan be adjusted via several approaches: through the initial density ofmetallic particles on the carbon allotrope, through the concentration ofthe metal-decorated allotrope starting material, through theconcentration of the unreduced metallic precursor starting solution, andthrough use of a competing seed site which gives rise to a heterogeneousbatch composition of nanowires both attached and unattached to carbonallotropes. Uniformity of the aspect ratio of nanowires is dependent onthe dimensions of the metallic crystalline seed. The aspect ratio of thenanowires can be controlled via selection of the diameter of nanowireand the ratio of carbon allotrope, and the metallic nanowire density isvery easily controlled via the initial concentration of surface zerovalent nanoparticle density on the carbon allotrope at the inception ofreaction.

The use of carbon allotropes as anchors for the metallic nanowire growthalleviates processing problems encountered with pure nanowire additives,especially inhomogeneous dispersion difficulties. The homogenousdispersion of carbon allotropes into polymeric matrices has already beengenerally mastered by those of ordinary skill in the art, and the knowntechniques can be directly applied to the nanowire-carbon allotropecomposites. The nanowires synthesized on the surface of the metaldecorated allotropes are readily dispersed into the matrix as they areattached to the surface of the decorated carbon allotropes.

Methods of embodiments of the invention allow for the creation ofmetallic nanowire decorated carbon allotropes using readily availablechemicals, modest reaction temperatures and time, ease of process andisolation, common laboratory equipment, and easy scale-up. The resultingmetal nanowire decorated carbon allotropes are useful in and ofthemselves as catalysts for a variety of chemical processes, and canalso be combined with polymeric or other materials to improve certainphysical, mechanical and/or electrical properties.

Embodiments of the invention cover many different combinations for bothmetal and carbon allotropes. The procedure described in detail belowutilizes silver for the nanowire synthesis, gold for the “metallicdecorations”, and multi-walled carbon nanotubes (MWCN) for the carbonallotrope. However, it should be appreciated that this specificcombination represents only one of many reaction possibilities. Forexample, zero valent metallic nanowires and/or nanorods may include,e.g., silver, gold, palladium, platinum, nickel, etc. Metallic decoratedcarbon allotropes, where M=zero valent metallic nanocluster, mayinclude, e.g., M-SWCN. M-MWCN, M-exfoliated graphite, etc. Whichevercarbon allotrope is used, the metal “decorations” will serve as the seedsites for nanowire/nanorod growth. The carbon allotrope will not affectthe chemistry that occurs with nanowire growth. As noted above, thedensity of the “metal decorations” can be varied. The density ofnanowires grown is dependent on the number of available sites and thesurface area exposure of such sites. The diameter of the metaldecorations will influence the resulting nanowire/nanorod diameter andthe length of resulting nanowires/nanorods. Of benefit, the large aspectratio moieties such as those prepared according to embodiments of thepresent invention give rise to material properties which are enhancedand superior with very low loading because of the tremendous surfacearea available for interaction.

Having generally described the invention, a more complete understandingthereof may be obtained by reference to the following exemplaryembodiment, which is provided for purposes of illustration only and isnot intended to limit the invention in any way.

An exemplary embodiment of the invention comprises silvernanowire-decorated multi-walled carbon nanotubes (Ag-MWCN). Materialsused in the example production of the silver nanowire-decoratedmulti-walled carbon nanotubes included ethylene glycol (EG) (99.8%anhydrous), poly (vinyl pyrrolidone) (PVP) (55,000 M.W.), silver(I)nitrate (AgNO₃, 99.97%), ethanol (95%), and gold-decorated multi-walledcarbon nanotubes (Au-MWCN). The gold-decorated multi-walled carbonnanotubes were prepared using the methods described in U.S. Pat. No.7,704,553 for use as the reacting substrate for directed metallicnanowire growth. It was believed that nanowire/nanorod growth occurredupon the nanometer-sized metal clusters, also known as “metallicdecorations.” These “metallic decorations” acted as metallic “seeds”upon which the continued metallic nanowire growth occurred. The diametersize of the metallic clusters available for surface reaction upon thecarbon allotrope influenced the diameter of resulting nanowires and/ornanorods. The poly (vinyl pyrrolidone) used in the silver nanowiresynthesis functioned as a passivating/capping agent. Passivation of ametallic face was believed to have rendered the passivated faceinactive, with the resulting suppression of cluster growth predominatelyseen for metallic silver. With passivation, the silver growth occurredon a non-passivated face, resulting in unidirectional, wirelike growthof silver.

The production of silver nanowire-decorated multi-walled carbonnanotubes began by, in a clean three-necked round-bottom flask, heating30 mL of EG to 165° C. with magnetic stirring by means of a silicon oilbath. In a volumetric flask, silver nitrate, 0.424 g (2.5 mmol), wasdissolved in 25 mL EG (0.1 M solution). In a second volumetric flask,55,000 M.W. PVP, 0.488 g (4.4 mmol) was dissolved in 25 mL EG (0.176 Msolution). Using an analytical balance, the quantity of Au-MWCN requiredfor [Au]=11 micromols was measured.

Once the stirring EU reached 165° C., Au-MWCN was introduced into thereaction flask. When an equilibrium temperature of 165° C. had beenmaintained for about five minutes, the silver nitrate solution was addedover 7.5 minutes dropwise via a syringe pump, from two 10-mL syringes(pump setting @ 1.2 mL/min). The solution appeared to turn a littleyellow upon addition of the silver solution, followed by yellowish-grayhue toward the end of reaction. Immediately upon the completion ofsilver solution addition, began the dropwise addition of the PVPsolution via syringe pump, from two 10-mL syringes (pump setting at0.4/min) The solution hue appeared iridescent and opaque, transformingto a creamy tan with silvery highlights after about thirty minutes ofreaction time. The reaction flask was removed from the heat after aboutone hour.

The product, Ag-MWCN, was purified by centrifugation at 2500 rpm forthirty minutes; the supernatant was discarded, the Ag-MWCN wascentrifuged twice more at 2500 rpm for thirty minutes in ethanol,discarding the supernatant each time. The Ag-MWCN was allowed to dry atroom temperature, leaving a gray powder remaining. Pentagonally twinnedsilver nanowires having diameters of approximately 100 nm (diameterscorresponding to the diameters of the metallic nanocluster“decorations”) and of an approximate length of 2 to 30 microns wereisolable. FIG. 1 shows a high resolution scanning electron micrograph(HRSEM) of a nanowire “decorated” substrate prepared in accord with theprocedure above, and it was also noted that no significant discernibledifference was observed over a preparation time range betweenapproximately 30 to 90 minutes.

Embodiments of the invention may be used for inorganic-organic hybridmaterials where the separate properties of carbon allotrope and metallicadditives are indicated for various applications that traditionallywould only include the selection of one additive or the other forinclusion into the host matrix material. The metal nanowire decoratedcarbon allotropes are useful as catalysts in a variety of chemicalreactions. The metal can be varied, and the aspect ratio of the nanowireprovides for very large surface areas while using small amounts ofpotentially expensive metals. These features are particularly attractivefor applications as catalysts in fuel cells, organic transformations andpolymerization processes. The unique attributes and variety in terms ofthe combination of properties that are achievable with these materialsalso points to their use in a variety of sensor applications. The metalnanowire decorated carbon allotropes can also be blended with polymersand other materials leading to unique combinations of physical,mechanical, electrical and thermal properties. This invention haspotential government and commercial, such as chemical, commodityplastics, pharmaceutical and biomedical, applications.

Some specific examples of potential uses for metal nanowire decoratedcarbon allotropes of embodiments of the invention include catalysts forchemical transformations, energy absorbing materials and energydissipating materials, selective gas and chemical sensors and as anantimicrobial agent, which is a common use of some zero valent metalssuch as silver, Metal nanowire decorated carbon allotropes ofembodiments of the invention may also be useful for organictransformations, fuel cells, catalytic polymerization, catalyticmembranes, heat sensing membranes, gas selective permeable membranes,and heat sensitive detecting membranes.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A method for preparing a metal nanowiredecorated carbon allotrope, the method comprising: providing a pluralityof seed templates, each seed template comprising a carbon allotropecontaining a plurality of metallic crystalline seeds; reacting theplurality of seed templates in a metal salt solution with a polymericpassivating reagent to form a zero-valent metallic nanowire from eachcrystalline seed; and recovering the metal nanowire decorated carbonallotrope.
 2. The method of claim 1, wherein the carbon allotrope isselected from the group consisting of buckminsterfullerene, carbonnanotube, graphite, and exfoliated graphite.
 3. The method of claim 1,wherein the metallic crystalline seeds are selected from the groupconsisting of silver, gold, platinum, palladium, and nickel.
 4. Themethod of claim 1, further comprising: controlling a diameter of themetal nanowires by controlling a diameter of the metallic crystallineseeds.
 5. The method of claim 1, further comprising: controlling adensity of the metal nanowires by controlling a density of the metalliccrystalline seeds.
 6. The method of claim 1, wherein the polymericpassivating reagent comprises poly (vinyl pyrrolidone).
 7. The method ofclaim 1 wherein the metal salt solution comprises a polyol solvent thatalso acts as a reducing agent.
 8. The method of claim 7, wherein thesolvent is ethylene glycol.
 9. The method of claim 1, wherein the metalsalt is silver nitrate.
 10. The method of claim 1, wherein the metalliccrystalline seeds and the metallic nanowires comprise a zero valencemetal.
 11. A method for preparing a metal nanowire decorated carbonallotrope, the method comprising: providing a plurality of seedtemplates, each seed template comprising a carbon allotrope containing aplurality of metallic crystalline seeds; reacting the plurality of seedtemplates in a metallic solution with a polymeric passivating reagent toform a zero-valent metallic nanowire from each crystalline seed; andrecovering the metal nanowire decorated carbon allotrope.
 12. The methodof claim 11, wherein the metallic solution comprises a metal salt. 13.The method of claim 12, wherein the metal salt is silver nitrate. 14.The method of claim 11, wherein the carbon allotrope is selected fromthe group consisting of buckminsterfullerene, carbon nanotube, graphite,and exfoliated graphite.
 15. The method of claim 11, wherein themetallic crystalline seeds are selected from the group consisting ofsilver, gold, platinum, palladium, and nickel.
 16. A method forpreparing a metal nanowire decorated carbon allotrope, the methodcomprising: providing a plurality of seed templates, each seed templatecomprising a carbon allotrope containing a plurality of metalliccrystalline seeds; reacting the plurality of seed templates in asolution, wherein the solution comprises at least one metal in a formand concentration that facilitates growth of nanowires and a polymericpassivating reagent to form a zero-valent metallic nanowire from eachcrystalline seed; and recovering the metal nanowire decorated carbonallotrope.
 17. The method of claim 16, wherein the at least one metal inthe solution comprises a metal salt.
 18. The method of claim 16, whereinthe carbon allotrope is selected from the group consisting ofbuckminsterfullerene, carbon nanotube, graphite, and exfoliatedgraphite.
 19. The method of claim 16, wherein the metallic crystallineseeds are selected from the group consisting of silver, gold, platinum,palladium, and nickel.
 20. The method of claim 16, further comprising:controlling a diameter of the metal nanowires by controlling a diameterof the metallic crystalline seeds.